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Re: [PATCH 2/8] x86/boot: Collect AMD speculative features earlier during boot
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 26 Jan 2022 13:37:35 +0000
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- Thread-topic: [PATCH 2/8] x86/boot: Collect AMD speculative features earlier during boot
On 26/01/2022 12:44, Roger Pau Monné wrote:
> On Wed, Jan 26, 2022 at 08:44:46AM +0000, Andrew Cooper wrote:
>> All AMD IBRS-related features are in CPUID.0x80000008.ebx. Collect them in
>> early_cpu_init() so init_speculative_mitigations() can use them.
>>
>> Rework the existing logic structure to fill in c->extended_cpuid_level and
>> separate out the ambiguous use of ebx in an otherwise 0x80000008-specific
>> logic block.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> It would be good to update the comment ahead of early_cpu_init to
> mention it now also gather speculation-related fields from CPUID in
> order to do early setup of mitigations.
>
> I think you could also use boot_cpu_data in spec_ctrl.c print_details
> instead of fetching again the cpuid leafs?
Hmm - I may have a mistake here.
Boot time CPUID handling is giant mess, and I haven't had time to finish
my work to make BSP microcode loading dependent on xmalloc(), allowing
it to move far earlier, and removing the early/late CPUID split.
However, init_speculative_mitigations() is called after late CPUID
setup, so e8b should be suitably collected. Let me try to figure out
what's going on.
For print_details(), I have a feeling that may have been an artefact of
an early version of the logic, and likely can be cleaned up.
~Andrew
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